The present invention generally relates to semiconductor optical apparatuses, and more particularly to a semiconductor optical apparatus that includes therein a laser diode and which is adapted for mounting upon a host apparatus with improved precision with respect to the position of the optical beam produced by the laser diode.
Various electronic apparatuses use a laser diode. For example, laser diodes are used in optical disk devices, laser printers and optical telecommunication apparatuses.
When using a laser diode, an example shown in FIG. 1 by a numeral 2, in such electronic apparatuses, it is necessary to determine the position of the luminous spot designated in FIG. 1 by a numeral 5 with a high precision, particularly with respect to the expected beam position designated by a numeral P. Preferably, the offset A in FIG. 1 indicative of the deviation of the optical axis is set below a few microns. Similarly, the offset B in the axial direction should be set below a few microns.
Thus, it is necessary to fabricate the laser diode with a high precision in terms of the outer dimensions.
Further, the laser diode is required to have a compact size.
FIGS. 2 and 3 show an example of a conventional laser diode assembly 1.
Referring to the drawings, the laser diode assembly 1 includes a laser diode 2 mounted within a metal case 3.
The case 3 is formed by machining and includes a disc part 3a and a projecting part 3b projecting from the disc part 3a.
As shown in FIG. 2, the disc part 3a is formed generally symmetrical with respect to a center line 3a.sub.-1 and has a surface 3a.sub.-2 that acts as a reference surface when mounting the laser diode assembly 1 upon other apparatuses.
It will be noted that the projecting part 3b carries thereon a heat sink 4, and the laser diode 2 is mounted upon the heat sink 4. In FIG. 2, the edge of the laser diode 2 from which the optical beam is emitted is designated by a numeral 5. Hereinafter, the edge 5 will be referred to as a luminous point.
Further, the apparatus of FIG. 2 includes lead wires 6 and 7 as well as electrode pins 8 for external connection, and the laser diode 2 is protected by a cap 9 that is formed with a window 10 for passing the optical beam. Further, there is provided an optical detector 11.
Referring to FIG. 3, it will be noted that the heat sink 4 is mounted upon the projecting part 3b.sub.-1 by a braze alloy layer 12, and the laser diode 2 itself is also mounted upon the heat sink 4 by another braze alloy layer 13.
In the laser diode assembly 1 having such a construction, it is preferred to determine the dimensions C, D and E as accurate as possible, preferably within the order of microns, wherein the dimension C and E represent the distance of the luminous spot 5 as measured from the center line 3a.sub.-1 in the Y- and X-directions, while the dimension D represents the distance of the luminous spot 5 measured from the reference surface 3a.sub.-2 in the Z-direction.
In the structure of FIG. 3, it will be noted that, because of the existence of the heat sink 4 and associated braze layers 12 and 13, there is a tendency that the distance C variates in the order of 100 .mu.m even when the position of the projecting part 3b is determined with a high precision.
Similarly, there is a tendency that the dimensions D and E vary in the Z- and X-directions respectively in the order of 100 .mu.m, due to the deviation associated with the mounting of the laser diode 2 upon the heat sink 4.
In order to overcome the foregoing problem, the laser diode assembly 1 is generally mounted upon an external host apparatus such as an optical disk apparatus 15 together with an adjusting mechanism as shown in FIG. 4.
Referring to FIG. 4, the laser diode assembly 1 is mounted upon a slidable plate 16 that acts as the adjusting mechanism, wherein the slidable plate 16 is mounted upon the external apparatus 15 by means of a screw 17. When mounting the laser diode assembly 1 upon the apparatus 15, the position of the apparatus 1 is adjusted in the X- and Y-directions to minimize the deviation for the dimensions C and E.
Further, the deviation with respect to the dimension D is compensated for by moving a collimator lens 18 in the Z-direction by actuating an eccentric cam 19.
Such a conventional laser diode assembly has an obvious drawback in that the apparatus requires a complicated adjusting process as well as mechanism when mounting upon the external apparatus 15. When the apparatus 15 is an optical pickup device, for example, such an adjusting process increases the number of steps that are needed to assemble the optical pickup device. Further, such a complex adjusting mechanism increases the size of the optical pickup device.
Further, it should be noted that the disk part 3a forming the case 3 of the apparatus 1 generally has a large diameter d which is as large as about 10 mm. Thereby, the apparatus 1 inevitably has a large size.